The applicant of the subject application has provided a compact actuator formed, as shown in FIG. 9, in combination of a guide mechanism 3 for guiding a sliding motion of a movable block 1 along a track rail 2 and a ball screw mechanism 4 for moving the movable block 1.
The track rail 2 is formed so as to provide a generally U-shape in section having a bottom portion and a pair of wall portions, and the movable block 1 is clamped between the opposing paired wall portions. The movable block 1 has a ball screw portion at its central portion, and is supported at its both side portions by the wall portions of the track rail 2. The ball screw portion of the movable block 1 is screw engaged with a screw shaft 4 penetrating the movable block 1. When the screw shaft 4 is rotated, the movable block 1 slides along the track rail 2. The movable block are formed, at its both sides, with loaded ball rolling grooves extending in the axial direction of the track rail 2 so as to provide a guide mechanism 3.
A number of balls are disposed to be rollable between the track rail and the movable block so that the movable block is smoothly slid along the track rail.
In such actuator, since the U-shaped track rail is adopted, high rigidity can be ensured in spite of a compact outer dimension, thus being advantageous.